This invention relates generally to optical lens systems, and, more particularly, relates to relay lens designs adapted for use in medical endoscopes.
Medical endoscopes are widely utilized to view internal regions of the human body during diagnostic, surgical, and other medical procedures. Endoscopes typically include a long, thin, rigid or semi-rigid optical cylinder affixed to a viewing mechanism. The cylinder is sufficiently narrow to be inserted through a small openings in the body, which may be natural or surgical. When the endoscope is inserted and positioned for use, an image of the object being viewed is formed at an inserted end of the endoscope by an objective lens. The image passes through a series of relay lenses down the cylinder to an eye lens or video camera at a viewing end of the endoscope.
The relay lenses must be very narrow and are typically around 2.4 mm to 3.0 mm in diameter, and 20 mm to 30 mm long. Each relay lens is usually made of two or more elements and a pair of two relay lenses make up a set of relay lenses. Most endoscopes require two or more sets of relay lens pairs for proper operation. The number of sets depends on the length and specific requirements of a particular endoscope.
Additionally, unique optical characteristics of each relay lens require specific spacing distances between a pair of relay lenses within a set, and between sets of relay lens pairs within an endoscope. The required distances are typically maintained by inter-lens spacers which may be hollow cylindrical elements.
Conventional relay lenses generally include one or two relatively thin end lenses affixed to a substantially thicker center lens. Where one end lens is affixed to a center lens the resulting relay lens is frequently referred to as a "doublet." Where two end lenses are affixed to opposed ends of a center lens, the relay lens is referred to as a "triplet." Both doublets and triplets are disclosed in U.S. Pat. No. 4,575,195 to Hoogland.
Problems associated with known relay lenses include the high cost of accurately affixing the end lenses to the center lens. Typically, lenses are assembled within standard optical "V-blocks", but the thin end lenses tend to be unstable unless mechanically supported within the "V-blocks" during cementing. The diameter-to-thickness ratio of most end lenses is roughly comparable to that of standard corrective contact lenses. The difficulty of affixing such end lenses is exacerbated in the manufacture of triplets because the end lenses have to be precisely aligned on the opposed ends of the center lens, such that all three lenses share a common central axis.
An additional problem associated with conventional relay lenses is the requirement that the relay lenses and inter-lens spacers be inserted into the optical cylinder of the endoscope in a specific alignment and in a specific sequence. Frequently, during assembly of the endoscope, relay lenses are inadvertently inserted in the wrong sequence, or in an inverted position. Moreover, inter-lens spacers are often inserted in an improper sequence. Such errors may not be detected until the endoscope is tested by an end-user. Disassembly and extraction of the lenses and spacers is a difficult, time consuming and costly procedure.
A further limitation of conventional relay lens configurations is the high cost of manufacture of the end lenses and center lenses. Center lenses, in particular, require very delicate procedures. They are relatively long, extremely thin, typically made of glass, and therefore, crack and break easily. Additionally, precisely curved lens surfaces must be formed on each end surface of the center lens. Moreover, some relay lenses utilize different end lenses attached to the same center lens. Essentially, they require manufacture of three separate lenses for each relay lens.
Thus, because of structural limitations associated with the relatively short axial dimension of their end lenses, conventional relay lenses are difficult to fabricate. Conventional designs require extreme care in assembly within an endoscope due to the varying alignment and space requirements of the relay lenses and inter-lens spacers. Moreover, they are costly to manufacture due to the relatively long axial lengths of their center lenses and the need for multiple lens surfaces.
Certain of these problems are overcome by the lens designs disclosed in U.S. patent application Ser. No. 07/507,877 filed Apr. 12, 1990 for Endoscope Lens System.
The endoscope relay lens designs disclosed in U.S. patent application Ser. No. 07/507,877 utilize symmetrical component configurations having a center element that is at least axially symmetrical. The central element can be, for example, semi-spherical ball element.
In particular, one embodiment disclosed in U.S. Ser. No. 07/507,877 is a Symmetrical triplet lens assembly in which the center lens is substantially spherical, the outer elements are identical to each other and very thick compared to conventional endoscope relay lenses, and the mechanical spacers between the relay lenses are all identical in length. This configuration assures proper assembly, in that the relay lens cannot be inserted backwards, and that no unique sequence of spacers is required.
However, in the configuration disclosed in U.S. Ser. No. 07/507,877, the outer elements are quite long, and therefore difficult to manufacture without further dividing the outer elements.
Accordingly, it is the general object of the present invention to provide improved endoscope relay lens configurations that overcome the problems associated with known relay lens designs.
It is a more specific object to provide an improved endoscope relay lens that has elements that facilitate assembly of the relay lens.
It is another object to provide an improved endoscope relay lens that facilitates alignment and spacing of the relay lenses within an endoscope.
It is yet another object to provide an improved endoscope relay lens that has elements that are substantially less expensive to manufacture than the elements of known relay lenses.
It is still another object to provide an improved endoscope relay lens that has optical performance characteristics that are substantially superior to the performance characteristics of known relay lenses.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.